1. Field of the Invention
Apparatuses and methods consistent with the present inventive concept relate to removing a transmission leakage signal in a radio frequency identification (RFID) reader.
2. Description of the Related Art
RFID is a wireless recognition technology for identifying and tracking a person, an object, or an animal by collecting information from an electronic chip (tag) attached thereto by using radio frequency (RF) waves. RFID is a main component of a ubiquitous sensor network (USN), that is, a network of intelligent sensors that integrates human, objects, and computers in various areas.
Unlike other mobile communication systems which use different transmission/reception frequencies, an RFID system uses a same frequency for transmitting and receiving signals and a signal may be transmitted simultaneously with receiving another signal. When different antennas are used for transmitting and receiving signals, the size of a transceiver module is larger, and a space for mounting the antennas and related costs increase.
In order to address this problem, a single antenna is used for both transmitting and receiving signals, together with a circulator or a directional coupler that separates transmission signals from reception signals behind the antenna. However, the circulator or the directional coupler is not an ideal device, and use of such device may lead to generation of a leakage signal when a transmission signal enters a path of a reception signal. Also, a leakage signal generated by a transmission signal may be input to a reception circuit due to impedance mismatch between a transceiver and the antenna.
The leakage signal generated by the transmission signal has a higher amplitude than a reception signal received via a tag and thus affects the reception signal, thereby decreasing a recognition rate of an RFID reader and generating problems such as linearity or noise in a reception circuit.
Accordingly, several methods of removing a leakage signal generated by a transmission signal in an RFID system including a circulator or a directional coupler have been proposed. In particular, in an RFID system that includes a directional coupler, the directional coupler has a smaller size and is cheaper than a circulator, and less circuits are additionally needed for removing a leakage signal. Thus, such RFID system may be used as a mobile RFID system.
However, in the case of an RFID system for an ultra high frequency (UHF) band, different frequency bands in the range of 840 MHz-960 MHz are used according to each country. Thus, an RFID system including a directional coupler cannot remove a leakage signal in all RFID bands used by different countries throughout the world, and in addition, the leakage signal cannot be removed when it varies according to environmental conditions. Thus, the use of such RFID system is limited.